After making lots of
fresh-squeezed juice, I reuse my citrus halves as pots for seedlings.
Just scoop out all of the remaining pulp and let the halves dry for a
few days in a dark dry spot. A few days later, just fill them with
potting mix and plant with fast growing seeds like sweet peas. No need
to poke holes in the bottom of the rinds since the dry skin of the peel
absorbs the moisture. I like to place my potted rinds in cupcake pans.